The present disclosure relates to image separation based multicolor document processing systems such as printers, copiers, multi-function devices, etc. and to control techniques for operating the same.
Real-time contone image paths operate only on individual image separations. Individual image separations divide a color image into at least the primary colors cyan, magenta, yellow and black.
System performance requirements and technology limitations have driven the printing industry to leverage the natural parallelism suggested by marking engine separations, utilizing independent communications channels to independent marking modules for each separation. That is, there is a primary marking engine for each of cyan, magenta, yellow and black. However, it has been found that the consideration of what other local colors are to be printed at a location, can improve print quality by the marking engine when printing its primary color. Such real-time controls within an image path have been shown to be beneficial in maintaining image quality, however the data isolation from such independent channels has bandwidth requirements which practically preclude processing calculations involving multiple color separations. A system needing to perform calculations using multiple image separations would need to incorporate a sophisticated memory sub-system, capable of providing the bandwidth required to bring the separations together in both time and space in the print engine. However, such a sub-system may incrementally increase costs and complexity. In addition to the memory components themselves, such a sub-system requires extensive control and data path functionality to effect the flows in and out, and a mechanism to enable the multiple flows to share the single memory. While the cost of the memory components has become much smaller and the cost of the considerable supporting logic is also dropping, the architectural and design complexity, board space, and power consumed are major incremental expenses unless there is some other reason to provide this buffering.
If such a memory buffer is already present in the design for some other purpose, leveraging it to enable cross-separation processing may dramatically increase the bandwidth or size requirements, and so its cost and complexity.
Cross separation calculations however may not require the full resolution of all separations. Low resolution separations of secondary colors use less memory than a full resolution separation of a primary color. Transmitting and storing only the low resolution data to a working engine prior to the cross separation calculation could allow the nominal full resolution data to be passed in real time without consuming buffer memory, resulting in less communication bandwidth and less memory use for the entire system. Less data communicated and less data stored results in less design time, less product cost, a smaller product, and a more reliable and efficient system.
One approach is presented in U.S. Patent Application Publication No. US2010-0103440 A1 by Crean, titled “Image Path Utilizing Sub-Sampled Cross-Channel Image Values” which is incorporated herein by reference in its entirety. This method and a system processes digital images using multi colorants and multiplexed sub-sampling. One color is retained at full nominal resolution and the remaining colors are sub-sampled. The full resolution nominal color values are used to search a lookup table based on known printing processes to normalize the sub-sampled colorants and produce desired output values. The drawback in such a technique is that the use of such a lookup table itself uses memory to store look-up data and to perform calculations using the complex formulas as featured in the U.S. Patent Application Publication No. US2010-0103440 A1. What is needed in the art is a means for producing the desired color pixel output result employing a multiplexing and sub-sampling solution without intensive memory requirements.
Accordingly, a need remains in the art for improved printing in high resolution which uses less buffer capacity and operates in a faster and cost effective manner. The present application presents such a system and method.